9701_s16_ms_33

Cambridge International Examinations

Cambridge International Advanced Subsidiary and Advanced Level

CHEMISTRY 9701/33

Paper 3 Advanced Practical Skills 1 May/June 2016

MARK SCHEME

Maximum Mark: 40

Published

This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the

examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the

details of the discussions that took place at an Examiners’ meeting before marking began, which would have

considered the acceptability of alternative answers.

Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for

Teachers.

Cambridge will not enter into discussions about these mark schemes.

Cambridge is publishing the mark schemes for the May/June 2016 series for most Cambridge IGCSE ® ,

Cambridge International A and AS Level components and some Cambridge O Level components.

® IGCSE is the registered trademark of Cambridge International Examinations.

This document consists of 6 printed pages.

© UCLES 2016 [Turn over

Page 2 Mark Scheme Syllabus Paper

Cambridge International AS/A Level – May/June 2016 9701 33

Question Indicative material Mark Total

1 (a) I Two burette readings and titre value given for the rough titre and initial

and final burette readings for two (or more) accurate titrations

II Titre values recorded for accurate titrations

and

Appropriate headings for the accurate titration table and cm 3 units.

• initial / start burette reading / volume / value

• final / end burette reading / volume / value

• titre or volume / FA 3 and used / added

• unit: / cm 3 or (cm 3 ) or in cm 3 (for each heading)

III All accurate burette readings are to the nearest 0.05 cm 3 .

Do not award this mark if:

• 50(.00) is used as an initial burette reading

• more than one final burette reading is 50.(00)

• any burette reading is greater than 50.(00)

• there is only one accurate titration.

IV There are two uncorrected accurate titres within 0.10 cm 3

• Do not award this mark if, having performed two titres within

0.10 cm 3 , a further titration is performed which is more than

0.10 cm 3 from the closer of the initial two titres, unless a further

titration, within 0.10 cm 3 of any other, has also been carried out.

• Do not award the mark if any “accurate” burette readings (apart

from initial 0 cm 3 ) are given to zero dp.

V, VI and VII Examiner rounds any burette readings to the nearest

0.05 cm 3 , checks subtractions and then select the “best” titres using the

hierarchy:

• two (or more) accurate identical titres, then

• two (or more) accurate titres within 0.05 cm 3 , then

• two (or more) accurate titres within 0.10 cm 3 , etc.

These best titres should be used to calculate the mean titre, expressed to

nearest 0.01 cm 3 .

1

1

1

1

3

Examiner calculates the difference ( δ) between the mean titres obtained

by the candidate and the Supervisor.

Accuracy marks are awarded as shown.

Award V,VI and VII for δ ⩽ 0.20 (cm 3 )

Award V and VI for 0.20 < δ ⩽ 0.40 (cm 3 )

Award V, only, for 0.40 < δ ⩽ 0.80 (cm 3 )

[7]

© Cambridge International Examinations 2016




(b)

Candidate must take the average of two (or more) titres that are within a

total spread of not more than 0.20 cm 3 .

Working / explanation must be shown or ticks must be put next to the two

(or more) accurate readings selected.

The mean should be quoted to 2 dp, and be rounded to nearest 0.01 cm 3 .

Two special cases, where the mean need not be to 2 dp:

• Allow mean expressed to 3 dp only for 0.025 or 0.075 (e.g.

26.325 cm 3 )

• Allow mean expressed to 1 dp, if all accurate burette readings

were given to 1 dp and the mean is exactly correct.

(e.g. 26.0 and 26.2 = 26.1 is allowed)

(e.g. 26.0 and 26.1 = 26.1 is wrong – should be 26.05)

1

Note: the candidate’s mean will sometimes be marked correct even if it

was different from the mean calculated by the Examiner for the purpose of

assessing accuracy.

[1]

(c) (i) (1.06/40) × 4 = 0.106 1

(ii)

(iii)

Correctly calculates

n(NaOH) = 0.106 × (25/1000) = 0.00265

and

n(HCl) = 0.00265

1

(iv) concentration FA 3 = 0.00265 × 1000/(b) 1

concentration FA 2 = concentration FA 3 × 10 1

All answers correct to 3 or 4 sf

(minimum of 3 parts attempted)

1

[5]

Question 1 [13]

2 (a) Table for results with

• Unambiguous headings and correctly displayed units

• Balance readings recorded to same no of dp

• One or two measuring cylinder readings recorded (does not have

to include volume collected)

• Unit: / g or (g) or in g (for each heading), allow grams / grammes

for g) and / cm 3 or (cm 3 ) or in cm 3 (for each heading)

• Calculates volume of gas/mass FA 4 to 3 sf.

1

Calculated value within 20% of supervisor value 1

[2]

(b) (i)

(ii)

Correctly calculates

• n(gas) = correct vol gas ÷ 24 000 to minimum 2 sf

and

• same number of moles of M 2 CO 3

1

(iii) M r = correct mass from (a) ÷ (ii) 1





(iv) A r = (M r -60)/2 to minimum 2 sf 1

Group 1 element identified as one with the closest A r and an explanation

e.g as it is the nearest

1

[4]

(c) (i)

% error = (1 × 100)/vol gas collected (if only volume collected shown in (a))

or (1 × 100)/final reading (when initial reading is zero)

or (2 × 100)/vol gas collected (if 2 readings)

1

(ii)

Reason:

gas dissolves (in water/solution) / reacts with water / water absorbs CO 2 1

Modification:

use a gas syringe / saturate water with carbon dioxide / use hot water / use

less water in tub / use smaller volume of more concentrated acid / use oil

(other non-aqueous solvent) instead of water

1

Reason:

gas escapes before stopper inserted / stopper not inserted quickly enough. 1

Modification:

viable means of keeping solid and acid separate before being added / use

larger lumps of solid / use more (excess) of a lower concentration of acid

1

[5]

Question 2 [11]




FA 5 is HCO 2 H; FA 6 is CH 3 CO 2 H; FA 7 is C 2 H 5 OH; FA 8 is C 6 H 12 O 6 ; FA 9 is Zn(NO 3 ) 2 .6H 2 O;

FA 10 is NaNO 3

3 (a) (i)

FA 5 FA 6 FA 7 FA 8

Fizz / bubbles /

effervescence

Gas turns

limewater

milky / cloudy

white / white

ppt / chalky

Silver / black /

dark grey and

mirror / solid /

ppt

Purple to

colourless or

solution /

MnO 4

– /

manganate

(VII)

decolourised/

disappeared

Fizz / bubbles /

effervescence

Gas turns

limewater

milky / cloudy

white / white

ppt / chalky

No reaction /

no change / no

silver mirror

No reaction

or

remains / turns

purple or pink

no change

No reaction/no

change

No reaction / no

change / no silver

mirror

Purple to

colourless or

solution / MnO 4

‒/

manganate(VII)

decolourised /

disappeared

no change

No

reaction/no

change

Silver / black /

dark grey

and

mirror / solid /

ppt

Purple to

colourless

or solution /

MnO 4

‒ /

manganate

(VII)

decolourised

/ disappeared

4

(ii) (–)CO 2 H / carboxylic acid 1

(iii)

(–)CHO / aldehyde / alkanal

or

alkene / C=C

1

(iv)

Oxidation of organic compound / reduction of MnO 4

−

/ redox

or

if alkene in (iii) then electrophilic addition

1

(v)

(–)OH / (1° / 2°) alcohol / alkanol / hydroxy

or

alkene / C=C

1

(vi)

Add Na to give effervescence / hydrogen / gas which pops with lighted

splint, or

Add PCl 5 / SOCl 2 to give misty fumes / steamy fumes / HCl , or

Add carboxylic acid AND (conc) sulfuric acid to produce fruity / sweet smell

or

if alkene in (v) Br 2 decolourised / brown to colourless

1

[9]




(b) (i)

NaOH

Al Effervescence / fizz /

bubbles

heat

FA 9 FA 10

No marking points for observations here

Fizz / gas / ammonia turns

litmus blue

Any 2 from:

• Melts / dissolves /

becomes liquid

• Condensation / steam

/ water vapour

• Brown gas / gas turns

litmus red

• Gas relights glowing

splint

• Solid turns yellow

Effervescence / fizz / bubbles

Fizz / gas / ammonia turns

litmus blue

Any 1 from:

• Bubbles

• Gas relights glowing

splint

• Melts / dissolves and to

yellow (liquid / solution)

4

(ii) Nitrate / nitrite 1

(iii)

Add named acid and (observe) brown gas for nitrite

or

Add (acidified) potassium manganate(VII) / KMnO 4 and purple to

colourless / decolourised for nitrite

1

(iv) No reaction for either so anion in each is nitrate / NO 3

‒ 1

[7]

Question 3 [16]


9701_s16_ms_33

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?